time domain transmissometry
TDT
The term time domain transmissometry (TDT) describes time measurement methods used to characterize the quality of signal transmissions.
In time domain transmissometry, the time required for an electromagnetic wave to propagate along a given length of the transmission line is measured. Similar to time domain reflectometry, a step pulse with a fast rise time is injected into an electrical conductor for this purpose. The step pulse propagates down the transmission line, and a voltage threshold is measured at the other end of the transmission line; however, the complex waveform analysis that is relevant to TDR measurements is usually omitted.
In the TDT measurement method, the focus is usually on determining the pulse transit time through the transmission line which allows, for example, an estimate of the dielectric constant of the medium. Time domain transmissometry is used, for example, in moisture measurement technology, the detection of defects, and tests of electrical transitions.
A typical soil moisture sensor that uses the accuracy of digitized time-domain transmissometry to provide an absolute measure of soil moisture under all temperature and soil chemistry conditions. Such digital TDT sensors have SDI interfaces that are used with appropriate data loggers. Only a low time resolution is required for such measurements. (© cronologic GMBH & Co. KG)